Apparatus for applying barrier coating substances to sheet materials

ABSTRACT

A barrier coating of the high viscosity &#39;&#39;&#39;&#39;hot melt&#39;&#39;&#39;&#39; class is applied with high uniformity to a moving web by means of a coating apparatus which is capable of operating at speeds as high as 1,500 feet per minute utilizing &#39;&#39;&#39;&#39;hot melt&#39;&#39;&#39;&#39; compounds of viscosities ranging as high as 100,000 c.p.s. The coating fluid in a heated condition is applied from a coating head consisting of a tubular body formed with an elongated aperture over which the web is passed. The coating fluid is under relatively high pressures of varying intensity. Pressure change along the elongated aperture is controlled by regulating web pressure. Multiple tensioning means are arranged at two opposite sides of the coating tube. One tensioning device engages the web at it approaches the coating head and acts initially to exert cross tension and stretch the web sufficiently to overcome variations in caliper and web length. A second tensioning device exerts linear tension to force the transversely stretched web uniformly against the coating tube with sufficient web pressure to equalize and balance pumping pressure of fluid all along the coating aperture. Required web pressures of a magnitude necessitating linear tension in excess of the tensile strength of any given web is provided by means of a web press roll adjustably supported in rolling contact with the web immediately above the elongated tube aperture. The web press roll is adjustable both vertically and horizontally to vary its position relative to the elongated tube aperture.

[ Dec. 17, 1974 APPARATUS FOR APPLYING BARRIER COATING SUBSTANCES TOSHEET MATERIALS Inventor: George C. Park, North Reading,

Mass.

Assignee: Bolton-Emerson, Inc., Lawrence,

Mass.

Filed: Feb. 22, 1973 Appl. No.: 334,747

Related US. Application Data Continuation-impart of Ser. No. 259,072,June 2, 1972, abandoned, which is a continuation-in-part of Ser. No.48,660, May 15, 1970, abandoned, Division of Ser. No. 806,473, March 12,1969, Pat. No. 3,556,832, which is a continuation-in-part of Ser. No.806,040, March 6, 1969, abandoned. which is a continuation of Ser. No.335,67, Jan. 3, 1964, abandoned.

US. Cl. 118/34, 118/410 Int. Cl. 1305c 5/02 Field of Search 118/33, 34,410, 411, 122, 118/8, 6; 226/39, 195

[56] References Cited UNITED STATES PATENTS 579,043 3/1897 Cloudman118/122 X 1,949,237 2/1934 Bradner 226/195 X 2,309,981 2/1943 Randall118/410 2,464,771 3/1949 Van Guelpen 118/410 2,727,488 12/1955 Nerim118/4'10 3,180,548 4/1965 Stafford 226/195 Primary Examiner.lohn P.McIntosh Attorney, Agent, or FirmMunroe H. Hamilton 5 7] ABSTRACT Abarrier coating of the high viscosity hot melt" class is applied withhigh uniformity to a moving web by means of a coating apparatus which iscapable of operating at speeds as high as 1,500 feet per minuteutilizing hot melt compounds of viscosities ranging as high as 100,000c.p.s. The coating fluid in a heated condition is applied from a coatinghead consisting of a tubular body formed with an elongated aperture overwhich the web is passed. The coating fluid is under relatively highpressures of varying intensity. Pressure change along the elongatedaperture is controlled by regulating web pressure. Multiple tensioningmeans are arranged at two opposite sides of the coating tube. Onetensioning device engages the web at it approaches the coating head andacts initially to exert cross tension and stretch the web sufficientlyto overcome variations in caliper and web length. A second tensioningdevice exerts linear tension to force the transversely stretched webuniformly against the coating tube with sufficient web pressure toequalize and balance pumping pressure of fluid all along the coatingaperture. Required web pressures of a magnitude necessitating lineartension in excess of the tensile strength of any given web is providedby means of a web press roll adjustably supported in rolling contactwith the web immediately above the elongated tube aperture. The webpress roll is adjustable both vertically and horizontally to vary itsposition relative to the elongated tube aperture.

1 Claim, 23 Drawing Figures PATENTEU SEC! H974 sum 01 0F 13 PAIENm, DEC!H914 sum on HF 13 PATENTEU SEC] 7 m4 SHEET 05 0F 13 PATENIEE SE31 7 I974sum 07 [1F 13 PATENTH, LIB! H974 S EET 0a or 13 PAIENIEB 353 saw us or13 PUMP OUTPUT SETTING POUNDS PER MINUTE WEIGHT l5 LBS. 3000 FT.

TARGET COATING SPEED OF WEB WEB WIDTH APPARATUS FOR APPLYING BARRIERCOATING SUBSTANCES TO SHEET MATERIALS This application is acontinuation-in-part of Ser. No. 259,072, filed June 2, 1972, nowabandoned; which in turn is a continuation-in-part of Ser. No. 48,660,filed May 15, 1970, now abandoned; which in turn is a division of806,473, filed Mar. 12, 1969, now US. Pat. No. 3,556,832; which in turnis a continuation-in-part of Ser. No. 806,040, filed Mar. 6, 1969, nowabandoned; which in turn is a continuation of Ser. No. 335,607, filedJan. 3, 1964, now abandoned.

The present invention relates to apparatus for applying a barriercoating substance to sheet materials of the class including paper webs,films, foil, fabrics, and the like. More particularly, the invention isconcerned with a coating apparatus of the class in which a coatingtubular coating head including an elongated discharge aperture isemployed. It is contemplated that the coating substance may be appliedas a single coating or in the form of successive coatings, one appliedto function as an outer protective surface on one or both sides of asinglr layer of material. The coating substance may also be employed asan adhesive or bonding agent for laminating two or more webs of materialtogether.

In coating a web of material with a slotted coating tube'throughopposite ends of which a high viscosity coating fluid is forced, acommonly experienced difficulty is failure to apply the coating in auniform thickness all the way across the web. This may occur largelybecause of pressure drop toward the center of the tube due to increasedfriction. As a result, greater internal pumping pressure is exerted atthe outer ends of the tube aperture or slot than at the center.

While such difficulties are subject to some degree of control when usingordinary solvent and emulsion-type coating materials applied atrelatively low flow rates, a much greater problem is present whendealing with high viscosity materials discharged at relatively highpressures to provide increasing higher flow rates. Under such conditionsgreater web pressure, normally induced by increasing linear tension,becomes necessary to maintain the web against the coating tube or headand for some coating operations, the requirement for added tension mayexceed the tensile strength of the web with consequent breaking.

A further condition which manifests itself is the tendency for highviscosity material supplied at higher flow rates to displace anyportions of the web which are slack or which are subject to bariationsin caliper or length. Furthermore, substantially increased tensionforces exerted linearly of a web having a slack or nonuniform portionsmay tend to draw the web undesirably and in this way also unsatisfactorycoating will occur.

It is, in general, therefore, a chief object of this invention to dealwith the problem indicated above, and to provide an improved apparatusfor applying barrier coating substances of relatively high viscositiesutilizing a tubular type coating head. It is a further object of theinvention to devise a coating apparatus which includes novel means forcontrolling webpressure and web tension in combination with a tubulartype coating head and to utilize the coating apparatus in coatingthermoplastic compounds of the class commonly referred to as hot meltcompounds which may have relatively high viscosities in a viscosityrange running as high as 100,000 c.p.s.

Another object of the invention is to devise apparatus for applying highviscosity coatings to webs which are subject to variation in caliper andlength in order to insure application of highly uniform layers andelimination of streaks or lines resulting from particles being collectedin the coating equipment.

Another object of the invention is to provide a coating apparatus bymeans of which web speed and pumping rates may be synchronized and acontinuous indication of both web speed and pumping rates may bevisually presented to a machine operator so that a more efficientcoating operation may be realized.

Still another object of the invention is to provide a modification ofthe coating apparatus of the invention in which a means for impartinginternal tension to a web is provided. I

The nature of the invention and its other objects and novel featureswill be more fully understood and appreciated from the followingdescription of a preferred embodiment of method and apparatus selectedfor purposes of illustration and shown in the accompanying drawings inwhich:

FIG. 1 is a plan view illustrating schematically a web and apparatusemployed in coating the web with a high viscous coating material;

FIG. 2 is a side elevation view further illustrating a web movingthrough the coating apparatus of the invention and particularlyindicating multiple tensioning means;

FIG. 3 is a front elevational view of the apparatus shown in FIG. 2;

FIG. 4 is a vertical cross sectional view showing details of the tubularcoating head and a web in a coating position;

FIG. 5 is an enlarged vertical cross sectional view further illustratingportions of the coating head and web of FIG. 4;

F IG. 6 is a fragmentary cross sectional view of the applicator headtaken approximately on the line 66 of FIG. 9;

FIG. 7 is a cross sectional view of a tubular component shown removedfrom its supporting structure;

FIG. 8 is a fragmentary elevational view of the coating head shown withheating means associated therewith;

FIG. 9 is a cross sectional view taken on the line 9-9 of FIG. 8;

FIG. 10 is a cross section taken approximately on the line I0 l0 of FIG.9;

FIG. 11 is an exploded view of the coating head components, portions ofwhich are indicated fragmentarily;

FIG. 12 is a fragmentary detail plan view illustrating a web of paper inan operative position relative to the coating tube;

FIG. 13 is a plan view illustrating diagrammatically power drivencomponents of the coating apparatus connected in interlocking drivingrelationship for syn chronizing web speed and pumping rates in avisually indicated manner;

FIG. 14 is a cross section illustrating diagrammatically a multiplecoating operation;

FIG. 15 is a detail cross sectional view of a modified form of coatinghead apparatus which includes a special web press roll member;

FIG. 16 is a fragmentary elevational view further illustrating thecoating head and web press roll apparatus of FIG.

FIG. 17 is a detail cross sectional view illustrating diagrammatically aweb fibre ironing step;

FIG. 18 is a diagrammatic view illustrating an operators chart for onespecific coating operation;

FIG. 19 is a plan view illustrating schematically a web coatingapparatus having an internal tensioning and clutch mechanism forregenerative braking;

FIG. 20 is a perspective view illustrating diagrammatically theapparatus shown in FIG. 19;

FIG. 21 is a side elevational view of a coating machine in which theapparatus of FIG. 19 is contained;

FIG. 22 is a side elevational view of an opposite side of the coatingmachine of FIG. 21, and

FIG. 23 is a fragmentary detail view of portion of the clutch and gearmechanism shown in FIG. 21.

As earlier noted, the coating method and apparatus of the invention inone preferred embodiment is designed to handle hot melt materials of theclass which may require heating to temperatures as high as 400 F andwhich may occur in a viscosity range running as high as [00,000 c.p.s.The invention will, therefore. be described with reference to the use ofthese high viscosity coating materials although it should be understoodthat this is not done in a limiting sense and various other classes ofcoating materials may be employed in the invention method.

With this preferred embodiment of the invention method, it iscontemplated that webs may be coated in a range of widths of from 15 to85 inches up to 200 inches at speeds running as high as 1,500 feet perminute and providing coating weights of from 2 lbs. up to 40 lbs. ormore. Coating may be applied to cover one side or two sides of a web andthe method may also be employed to coat, laminate with a second web, andagain coat, all in one pass through the machine.

In carrying out the method in its preferred form and handling highviscosity coating materials, I have discovered that I may employspecially controlled web tensions and web pressures in combination witha tubular type coating head and I have devised as one important featureof the invention multiple tensioning means arranged at two oppositesides of the coating head in relatively depressed positions.

The multiple tensioning means acts on the web as it leaves a supply rolland approaches the coating head under linear tension. Then just beforeand just after the head transversely directed tensioning forces stretchthe web transversely in sufficient degree to overcome variations incaliper and length of the web.

This cross tensioning step of the invention is essential to successfuluse of linear tension and linear tension as further exerted through themultiple tensioning means acts to force the transversely stretched webuniformly against the coating head with adequate pressure to equalizeand balance variable pumping pressures of high viscosity fluid along thecoating head and thus the problem of pressure drop from friction may becontrolled.

I have further discovered that in some coating operations, where veryhigh viscosities and high flow rates may require web pressures of amagnitude necessitating linear tension in excess of the tensile strengthof the web, I may provide additional web pressure at the coating head byemploying a special web press roll supported in rolling contact with theweb immediately above the coating head aperture and adjustable bothvertically and horizontally relative to the coating head.

I have futher determined that in controlling web tension and webpressure in the manner disclosed, it is important to maintain web speedand pumping rate in constantly regulated relationship to one another inorder to apply precisely controlled coating weight to the web.

In this connection, I have still further devised a novel interlockingdrive mechanism for actuating both web winding means and fluid pumpingmeans so that web speed and pumping rate in pounds per minute may besynchronized in ,a desirable manner.

I have still further devised a unique flowmeter and indicator apparatusby means of which the synchronized web speed and pumping rate arevisually indicated to an operator at all times. For use with theindicator apparatus, I have in addition also provided novel chart meansfor monitoring machine operation in accordance with a desired coatingweight to be applied.

Considering in more detail. the apparatus of the invention, I employ acoating head having a tubular coating element formed with an elongatedaperture. Heated coating fluid is forced through opposite ends of thetube under pumping pressure. The heated coating fluid is dischargedthrough the elongated aperture from a confined space which issubstantially sealed at one side. Sealing is accomplished bycontinuously advancing portions of the web under tension and inoverlapping relation to opposite ends of the elongated aperture so thatmaterial is coated on the web at points inside of the edges of the webat all times.

Attention is directed to FIG. 1 wherein I have illustrated a supply rollE from which a web of material W is drawn off by winding roll means andsubjected to a coating operation to provide a coated material W1 havinga coating L at the underside thereof. The material W may consist of acellulosic web and the coating may consist of a thermoplastic coatingsubstance applied from the heated tubular coating head generallyindicated by arrow T and including a tubular coating element Tl. Assuggested diagrammatically in FIG. 1, heated coating substance of heavyviscosity may, for example, be delivered from a supply source S by apump P to the coating element T1. A heating medium such as a source ofsteam at H is arranged to provide a circulation of heat to aheat-conducting body in the tubular coating element Tl through inlets H1and H2 and an outlet H3. These components are further illustrated inFIG. 3 wherein the pump P and a container for coating substance areshown supported in bracket members 4 and 6 on frame side 2.

The web W is continuously advanced at desired speeds by winding rollmeans as R. R1 and R2 indicated at the upper right hand side of FIG. 1.Also provided is a variable speed power drive for controlling the webspeed through the machine. The variable speed power drive may, forexample, include a variable speed motor M which drives a shaft M1 havinga sprocket M2 and chain M3 in turn meshing with a sprocket M4 on a shaftMS of winding roll R.

In accordance with the preferred embodiment of the invention, I combinewith the web winding and coating head means referred to special multipletensioning means more clearly shown in FIG. 2 and constituting animportant and essential feature of the invention method. The multipletensioning means includes tensioning devices which are so designed andcombined with the coating head T that both variation in web caliper andlength as well as variation in pumping pressure at the coating head maybe simultaneously dealt with and controlled.

Attention is directed to FIG. 2 wherein it will be observed that the webW is drawn off from the supply roll E under a tension which is inducedby the power driven winding roll R at R/Rl and braked at R3/R4 which maybe of any given intensity common to typical winding speeds.

In addition to this winding tension, I provide for additional tensioningof the web by means of multiple tensioning devices located at eitherside of the coating head T and in depressed positions such thattensioning forces are exerted from points below the top of the coatingtube T1 in both cases.

The multiple tensioning devices are shown in detail in FIGS. 2 and 3together with the coating head T and web guiding means. As shown inFIGS. 2 and 3, a roll stand V supports a roll of material from which theweb W is continuously drawn off by a nip R/Rl passing through thebraking nip R3/R4 and then over preheating roll R4. These rolls aresupported between frame sides 2 and 2 having extensions 2a and 2b andbetween the extensions 2a and 2b are supported in a fixed positionopposite ends of coating head T.

Located in the frame extension at the righthand side of the coating headT as viewed in FIG. 2, is one of the multiple tension-compensatingdevices of the invention consisting in a cross tensioning roll assemblyF1 and located at the opposite side of the coating head T is a secondlinear tensioning roll assembly F2.

The cross tensioning roll assembly Fl includes as a principal componenta rotating bowed expander roll R5 which has opposite extremitiesreceived in bearings in a roll stand 100. The expander roll extremitiesare provided with independent vertical adjustment means 102 for raisingand lowering the roll R5. Also provided are lateral adjustment means formoving the roll R6 into and out of skewed position. Operating wheels'RWl are fixed to control rods as 105 having bevel gears 106 forfacilitating manual adjustment of the roll R5.

It is pointed out that the axis of rotation of roll R5 is locatedsubstantially below the top of coating head T but is in close proximityto this member so that as a result the web W is subjected to crosstensioning and transverse stretching forces and almost instantly whilein a stretched state the stretched web moves over and around the coatinghead T.

In thus subjecting the web to cross tensioning forces I may vary thestretching action by raising and lowering the roll R5 as may be requiredfrom time to time and I may also increase the cross tensioning action bymoving the roll R6 laterally into and out of skewed positions and I mayalso employ additional rolls in a skewed position.

The linear tensioning roll assembly F2 includes a roll member R6rotatably mounted in a roll stand 108 in suitable bearing members whichcan be adjusted toward and away from the coating head T by means of anoperating wheel RW. The linear tensioning roll R6 is located with itslowermost peripheral portion occurring well below the top of the coatinghead T so that a linear tensioning force can be exerted downwardly ofthe coating head T and more importantly while the web is in a crosstensioning or stretched condition constantly controlled by the bowedexpander roll.

I have determined that by combining the multiple tensioning means notedwith the coating head T in the relative positions to one anotherdescribed, a novel and important multiple tensioning effect is realized.This multiple tensioning acts on the web W as it leaves the supply rollE and approaches the coating headT and operates initially to exert crosstension force of a magnitude which may stretch the web transversely insufficient degree to overcome variation in caliper and length of theweb.

The controlled cross tensioning step of the invention is, as earliernoted, essential to successful use of linear tensioning of the web andmakes it possible for linear tension as further exerted by the assemblyF2 to force the transversely stretched web uniformly against the coatinghead with adequate pressure equalize and balance varying pumpingpressures developing along the coating head.

In controlling web tension and web pressure in order to overcomedifficulties arising out of the use of high viscosity coating materialutilized at relatively high flow rates there may develop conditionswhere the necessary web pressure requires a web tension which exceedsthe tensile strength of the web to be coated and frequent breakingortearing can occur.

To deal with thisproblem, I have devised auxiliary web press roll meansfor increasing web pressure against the coating head while stillregulatinglinear and cross tensioning in the web itself. A preferred webpress roll means is illustrated in FIGS. 15 to 17 adjustably mountedabove the coating tube T1, and includes essentially a web press roll androll-mount means in which the roll is adjustably supported for rotativemovement in varying positions relative to the coating tube T1. v

In the roll and roll mount structure referred to, there is included ashaft 132 together with means for adjusting the roll and shaft forwardlyand rearwardly relative to the coating head T1 as indicated by thehorizontal arrow in FIG. 15. I also provide means for adjusting theposition of the press roll and its shaft 132 upwardly and downwardly assuggested by the vertical arrow in FIG. 15, in order to exert varyingdegrees of pressure against the web W in any desired position ofhorizontal adjustment over the coating tube T1.

As one desirable form of roll mount means for accomplishing this dualadjustment, I may employ a pair of pneumatic cylinders 134 and 136adjustably mounted at opposite sides of the machine on the frame sides 2and 2' for movement forwardly and rearwardly into desired positions oflateral adjustment, as indicated in FIG. 15. At their upper extremities,the pneumatic cylinders may be either pivotally or slidably supported.Suspended from respective plunger elements of the pneumatic cylinders134 and 136 are elongated bearing blocks 133 and 135, better shown inFIG. 16. The elongated bearing blocks 133 and are slidably disposed onhorizontal guide rods as 138 and 140 which may be yieldably secured toadjacent portions of the frame sides 2 and 2. Formed through ends of theelongated bearing blocks 133 and 135 are openings for receivingtherethrough opposite extremities of the shaft 132.

By means of the mounting arrangement described, it will be readily seenthat in a coating operation where the web W is required to be pressedagainst the coating head T1, the roll 130 and shaft 132 may be adjustedinto any desired position of horizontal adjustment and thereafterpressure may be exerted through the pneumatic cylinders in any desireddegree to force the roll 130 against the web W.

It will be observed that in a vertically centered position of the pressroll over the coating tube T1, the axis of rotation of the press rolland the central axis of the tube T1 will lie in a common vertical plane.If, however, the press roll is moved forwardly or rearwardly, its axisof rotation will bein a vertical plane which occurs at one side of andin spaced relation to the common vertical plane noted above, and greaterpressure may then be exerted against one side or the other of thecoating head slot.

I have determined that for many highly viscous coating materials, andparticularly viscous hot melt substances of the elastomeric type, it isimportant to control the adjustment of the press roll relative to thecoating head slot, and I have found that positioning the web press rollin a forwardly located position, i.e., from right to left of the coatinghead T1, as shown in FIG. 15, and then exerting web pressure, providesin many cases clearly superior coating results, and particularly so,where in an instance, the axis of the press roll is positioned to lie ina vertical plane which passes through or very close to the lead-off edgeof the coating tube slot.

I have further found that in coating with some extremely difficultcoating materials, it is essential to use the combined horizontal andvertical adjustment of the web press roll in order to obtain asatisfactory coating application. In thus adjusting the web coatingroll, I may desire to use various other mounting arrangements withadjustments and I may desire to positively drive the press roll or tovary its diameter through a range of sizes.

l find that by thus combining web press roll pressure with crosstensioning and limited linear tensioning, the problem of web breakingcan be avoided with uniformity of coating thickness being effectivelymaintained, and I may also desire to employ the web press roll forvarious other coating requirements.

Considering in further detail the coating head assembly T, there isincluded in this assembly a tubular element Tl having a specially formedelongated aperture and adjacent land surface by means of which aprecisely metered quantity of coating substance supplied by the pump Pmay be applied to a web and desirably smoothed out. Numeral 40 denotesthe aperture which is more clearly shown in FIGS. 4-1 inclusive and islocated at the upper side of the tubular element T1.

The tubular element T1 is constructed as a cylindrical body which isopen at opposite ends and along its upper side. There is thus defined aconfined space having an aperture 40 as shown in FIG. 7. Opposite edgeportions of this aperture 40 are adapted to be secured incircumferentialy adjustable relation to one another by means ofadjustment screws as 42 located transversely through opposite sidewallsections as shown in FIGS. 4 and 7. By adjusting these screws the widthof the elongated aperture 40 may be varied as desired.

I also provide between these adjustable sidewall sections filler stripsas 44 (FIG. 6) which operate to close the aperture 40 at opposite endsof the tubular element so that the quantity of a coating to be appliedfrom the aperture 40 may extend over a greater or lesser area.

The aperture 40 is further defined by a special metering edgeconstruction including a relatively high leadon edge 46 over which a webof material is led to the coating substance, and a relatively lowlead-off edge 48 over which the web and an applied layer of material isled away.

It is pointed out that when a web is moving over the tube T1 therelative difference in height between the lead-on edge 46 and thelead-off edge 48 provides for the formation of a short restrictedpassageway into which freshly coated underside portions of the web maymove without the coating being drawn across a sharp edge. It will alsobe observed that this restricted passageway tends to become larger ifthe flow of the coating substance extruded through the aperture 40increases' In combination with this relatively lower lead-off edgeconstruction, I have further provided a novel land surface constructionwhich is denoted by numeral more clearly shown in FIGS. 6 and 7 andconsisting of a relieved relatively flat area which extends away fromthe aperture for a short distance to become terminated at a recessedportion 52. This land surface is designed to smooth and level a coatedsurface of a web passed thereover and to set the coating substancefirmly against the web.

Another feature of the invention is the provision of pressure equalizingmeans for the member T1 embodied in the construction and operation ofthe tubular coating apparatus T as shown in greater detail in FIGS.4-11, inclusive. As noted therein member T1 is located in a specialmounting assembly supported at the front of the frame as shown in FIG. 3in bearing plates l5, l7.

Included in this assembly is a heat conducting bed tube 15 which, asshown in FIG. 11, is formed along its upper and lower sides with curvedrecesses in which are supported respectively the tubular coating deviceT1 and a second tubular member T2. Opposite ends of members T1, T2 andbed tube 16 are received through collar members as 18 and 20 adapted tobe bolted to the bearing plates 15 and 17. Secured outside the ends ofthe bed tube 16 and tubes T1 and T2 are closure members 22 and 24.

As will be observed from an inspection of FIGS. 9 and 11, these closuremembers 22 and 24 are formed with internal passageways 22a and 24a whichcommunicate with tubular members T1 and T2. The closure members 22 and24 are further formed with central plug sections 22b and 24b which areconstructed and arranged to fit and seal respective opposite ends of asteam chamber 16a of the heat conducting member.

By means of this arrangement steam for heating the bed tube 16 may beintroduced through inlets H1, H2 into a steam chamber 16a and removedfrom an outlet H3. There is thus provided a means of transmitting heatto such of the tubes T1 and T2 in order to maintain at a desiredtemperature a body of coating substance in the tubes T1 and T2.

As shown in FIG. 3, a supply of the coating substance is pumped from thesupply source S by pump P through a feed pipe 30 (FIG. 9) intopassageway 22a. Valve V opens and closes the feed pipe while V providesfor recirculating material through pump and strainer. A portion of thecoating substance passes from passageway 22a into the tube T1 whileanother portion of the coating substance passes through the tube T2 intothe passageway 24a and then into an opposite end of tube T1. With thisarrangement, it will be observed that there is no opportunity forpressure to drop from frictional losses in forcing material into tubeT1.

A further feature of the coating means of the invention is thearrangement of parts in the tube Tl. As noted in FIGS. 6 and 7, the tubeT1 is split along its upper side and formed with a kerf K at its bottomside so that the split may be opened or closed by turning adjustmentscrews 42. The pressure thus exerted squeezes the tiller strips 44 toprevent escape of liquid material at these points. Opposite ends of T1are further fitted with sealing rings which seal against end closuremembers 22 and 24.

In some coating operations where conditions tend to increase thelikelihood of streaks or ridges in an applied coating, I may desire tocombine with the coating tube Tl a special coating leveller device whichis illustrated in FIG. 4. This device includes an adjustable block 120mounted in close proximity to tube T1 and having adjustably securedtherein an L-shaped bar 122 mounted over a tube 124. Formed in theL-shaped bar along one edge is a V groove 126 in which'is looselycontained a levelling rod 128. I find that this levelling device may beset to engage a freshly coated web and the loosely disposed rod willfunction to spread out small quantities of fluid which accumulate as asmall excess body 130 all along back of the rod and this excess bodytends to provide a uniform levelling action of a desirable nature.

In carrying out the method of the invention, a supply of high viscosityheated coating substance is pumped into the tubes T1 and T2 to provideuniform pressure all along tube T1. The coating substance is constantlymaintained at a desired temperature by the heat conducting tube 16. Atthe same time, the web W of paper is guided into contact with a nip rollR3 and a preheating roll R4 and then through the multiple tensioningmeans and coating head T as earlier described. At this point the web iscaused to move through an arcuate path of travel which provides for apredetermined amount of contact of wrap-around of the paper with respectto the tube T1 and which may extend over an arc of 45 degrees or more. Adesired tension is exerted in the web and pressure is exerted by the webagainst the coating head slot. If the tension requirements causebreaking of the web, then the press roll arrangement of FIGS. to 17 isutilized.

It is pointed out that the wrap-around of the web may be controlled tonot only convert the tube T1 into a closed container with resultantpressure equalization, but may also provide a highly beneficial effectin laying down heated fibres of rough surfaced webs immediately prior toapplication of coating. This prevents fibres from remaining erect andpenetrating the coated layer to permit wicking and thus destroy thebarrier properties of the coating. This fibre-ironing action is villustrated diagrammatically in FIG. 17 in which fibres 120 in a web W6are laid down and held while coating layer 122 is applied from coatingtube T1.

As shown in FIG. 12, for a given width of a web W which is to be coated,the length of aperture 40 is controlled by use of filler pieces 44 sothat opposiste edges of the web W will overlap the filler strips andwhen held under a suitable tension will tend to seal the area ofelongated aperture 40 and constitute the space within the member T1 as aclosed volume. By this means uncoated strips may be left on the web witha minimum of difficulty.

In accordance with a preferred form of the invention, the pump P isregulated so that a substantially constant rate of flow of coatingsubstance is delivered to the member T1 and at a predetermined pressurewhich is of a magnitude such that it exceeds slightly the radiallyinwardly directed force component of the tensioned web of paper W.Pressure thus induced raises the paper a distance above the aperture 40which generally corresponds to the thickness of a layer of coatingsubstance desired to be applied to the underside of the paper. In thisway, I am enabled to apply only a desired amount of coating substanceand the web is never flooded and therefore does not require scrapingwith a doctor blade.

As this metered quantity of coating is removedfrom the top of the bodyof coating substance in opening 40 and applied to the web, it is almostinstantly moved in over the relatively low lead-off edge 48 and thenthrough the short restricted passageway comprised by the land surface 50and the moving web itself. While passing through this passageway, thecoating is levelled, compressed and smoothed against the land surface 50and set into the paper to eliminate any irregularities. A desirableresult of this passageway is that small particles which may occur in thecoating substance are carried off in the coated layer without collectingon the lead-off edge to cause streaking.

In thus providing the passageway noted, I have found that improvedresults may be obtained by having the lead-off edge 48 spaced lower thanthe lead-on edge 46 a distance lying in a range of from .005 to .007inches. A typical coating weight resulting from a pumping rate employedin forcing the coating material through the elongated aperture 40 may beexpressed as quantity of material applied, e.g., as 5 pounds perthousand square feet for a 60-inch web travelling at a rate of 600 feetper minute. This provides a coating thickness of approximately 0.001inches. An optimum land surface is one extending for a distance ofone-eighth inch between the lead-off edge 48 and the point of recesswhich forms the surface 52. The web is in contact with the coating tubeT1 a total not exceeding one and three-quarter inches in the directionof its movement.

The web with coated layer L leaves the tube T1 somewhat abruptly at thepoint of the recessed part 52 after having passed along the land surface50. Further movement is in a straight path of travel to the roll T6 fora short interval of time after which the web is turned and guided in areversed path of travel. This reverse path of travel coming immediatelyafter the coating step tends to extend and stretch the coating L in adesirable degree. After having thus been turned the web and thestretched coating thereon passes to roll T1 and then to roll R which isconstantly cooled to a desired temperature whereby the layer L of coatedsubstance may be shock chilled and set to a desired condition whilestill in a relatively stretched state.

The combined effect of reversing the web to stretch the layer L andalmost immediately thereafter shock chilling the partially set orhardened material prevents any tendency for curling of the paper todevelop as the layer L becomes fully conditioned. As a result, I may, bycontrolling the stretching of the layer and its time of setting providea paper stock which will remain flat in sheet form.

While satisfactory results for some coating operations may be achievedusing the equipment as described above, I have determined that in manycases where high viscosity coatings are applied at relatively high flowrates, a more precise control of web speed and pumping rates is requiredfor most efficient ma chine operation. With this in mind, I have furtherdevised a method and means for synchronizing web speed and pumping ratein pounds per minute in an accurately controlled manner.

Attention is directedd to FIG. 13 wherein I have illustrated anarrangement for interlocking the actuating means for a pump P1 with thedrive means for winter rolls R10, R11, R12. As shown in FIG. 13 avariable speed motor 140 drives a shaft 142 having a sprocket 144 and achain 146. The chain 146 meshes with a sprocket 148 on shaft 150 whichcarries winding roll R10. A sprocket 152 on shaft 150 drives a chain 154which in turn drives a sprocket 156 on a shaft 158. The shaft 158 isconnected to a variable speed transmission member 160 in turn connectedto shaft 162 coupled to the pump drive 164. By means of the arrangementdescribed, the pump rate in pounds per minute can be set to a desiredvalue for any given web speed and the two will then move in constantlymaintained synchronized relationship.

I find that this synchronized operation performs very satisfactorilywith the multiple web tension and web pressure controls earlierdescribed to control coating weight uniformly.

I have also devised special indicator means including a flow-meter 170connected into the pumping line to the tube T1 as shown in FIG. 13 andhaving a connection to an indicator device 172 which automaticallyindicates pumping rate in pounds per minute in response to changes inthe flow-meter readings. Also combined with the indicator device 172 isa second indicator means 174 which, by means of a suitable tachometerdevice, senses the rate of speed of the shaft 150 and translates thespeed into a reading of feet per minute of travel of web W4. Thus itaffords a convenient and extremely useful indicator for visuallyindicating to a machine operator readings in web speed and pumping rate.

In a typical instance of carrying out a coating operation with mechanismfor synchronizing both web speed and pumping rate as described above, aroll of material is put in place in the roll stand V. A web of thematerial is drawn off at a desired web speed and limited tension isexerted by the multiple tensioning means of the invention until the webruns through without the edges being skewed. Then the pump speed is setto operate at a rate which will furnish a required coating weight inpounds per square feet. Thereafter linear tension is increased graduallyuntil the longitudinal cross section profile of the web is unifomi. Thisis determined by blanking or cutting out small samples of the coated weband weighing these samples to check on uniformity. Finally with webspeed, linear tension and pumping rate adjusted correctly,cross-tensioning is adjusted to provide a uniform cross section profileas determined by cutting samples a second time and checking theirweight. In FIG. 1, one form of cutout samples Y are indicateddiagrammatically to illustrate these profile measuring operations. Withthese conditions having been established, I may increase or decrease thepumping rate to obtain heavier or lighter coatings as desired withuniformity being preserved.

I also provide chart means for use with the indicator device describedand one typical chart is illustrated in FIG. 18. As shown therein thechart presents tabulated data in the form of pounds of coating materialapplied per minute for any given set of web widths and web speeds. Byinspecting a chart of this nature for any specific coating operation,theoperator may readily adjust the pumping rate to a required value toobtain the coating weight desired. It will be understood that for eachcoating weight desired, there will be a separate chart to be referred toas desired. This system of measuring flow rate and web speed lendsitself readily to automation.

In FIG. 14, I have illustrated a method of applying successive coatings,one over another, using thetension control devices and coating head ofthe invention. I have found that by applying a heated coating of a highviscosity hot melt compound as described, it becomes possible for afirst coating, while still in a partially set and slightly tacky state,to move over the coating head and pick up another layer of coatingmaterial which is controlled as before by the web pressure andsynchronized pumping speed and web speed. As a result, I maysuccessively apply different types of barrier coatings with excellentresults.

FIGS. 19 to 23 illustrate a modification of the invention wherein l havedevised a method of differential tensioning. In this method, variationin linear tension may be induced and localized at two or more separatesections of a moving web. In carrying out my method of differentialtensioning, the moving web is constantly engaged between two nip pointscomprised by a set of pull rolls and a set of braking rolls. The twosets of rolls are, however, geared together in a novel manner so thatthere is induced a predetermined surface speed differential between thepull rolls and the braking rolls.

In thus varying tension in two or more separate sections of a movingweb, the braking rolls are comprised by a novel clutch assemblyincluding two clutch sections both of which sections are always rotatingbut at different speeds. Increase in tension with this arrangement isrealized by increasing pressure of one clutch section against the other,and in a preferred form of my method, increase in pressure isaccomplished by the use of compressed air. It will be understood that inthus increasing pressure on the clutch faces, a small slipping factor ispresent which is reduced until the clutch faces approach fullnon-slipping engagement.

An important feature of my method of differential tensioning resides inthe fact that both clutch sections are rotating, and although rotatingat different speeds, the percentage of slip between the sections is verylow, i.e., about 6 to 8 per cent and therefore the heat dissipationfactor is minimal. This is signficant from the standpoint of paper websespecially since most paper webs are capable of undergoing from 2 to 3per cent without breaking.

1. Apparatus for applying a viscous coating of the hot melt class to aweb of material, said apparatus comprising a frame, a supply roll memberfor supporting a wound roll of the material at one end of the frame,winding roll means mounted at an opposite end of the frame, powerdriving mechanism for actuating the winding roll and drawing off a webof the material at a desired rate of travel, a coating tube arranged inthe frame below the path of said web to engage the web, said coatingtube being constructed with a curved upper side and having an elongateddischarge aperture formed along said upper side and lying within theconfines thereof, said aperture having high lead-on edge and a lowlead-off edge, tension roll means located both in advance of, and inrear of, said tube on said path for exerting tension in the web andguiding the web in an arcuate path of travel over said curved upper sideand over said lead on and lead-off edges, a roll mount structure, apress roll rotatably supported in the roll mount structure above thecoating tube in rolling engagement with the web and forming a pressurenip with said tube, and said press roll having its axis of roTation inrear of said lead on edge directly above said lead-off edge and lying ina vertical plane which passes through the lead-off edge of the elongateddischarge aperture.